Prior as well as current designs of rotary couplers have the head portion of the coupler assembly formed with the shank much like the standard AAR E and F type couplers. In these prior art constructions, a major portion of the shank extends from the coupler head into a mating segment of the shank or into a special yoke construction in order to permit rotation of the coupler head. These constructions are subject to jamming and sticking when the relatively small bearing surfaces on the shank become worn or contain foreign matter, or both, which causes difficult rotation of the railroad cars in their intended function. By placing the rotating element of these coupler constructions in the small physical confines of the shank, the loads applied to the small parts are substantial due to normal loading forces involved in typical train action as well as the added forces encountered from the rotating action. A difficulty with the prior art constructions is that they require frequent maintenance attention due to wearing of the parts and this presents some difficulty because the parts are contained within the confines of the railroad car sill structure, thus not readily accessible.
Another disadvantage of the current and the prior art rotary couplers is that they sometimes inadvertently uncouple when rotated if the standard coupling mechanism is utilized. Because of the vibrations and other extrinsic forces that may act on the coupler when a railroad car is rotated to an inverted position, the couplers may become disconnected. When this occurs the train must be recoupled before proceeding with the unloading operation. Some prior art rotary couplers are constructed to be permanently connected so that once the train is made up and the cars are connected, they normally remain in the connected condition. This overcomes the difficulty in inadvertent uncoupling, however, it presents some difficulties when intentionally uncoupling the train due to the nature of the semi-permanently connected couplers.